Rotaviruses are the single most important cause of childhood viral gastroenteritis in the developed and developing countries. It is estimated that over one million diarrhea-related infantile deaths that occur annually are directly related to rotaviruses. The urgent need for a rotavirus vaccine has been recognized, but for a number of factors, such a vaccine is not yet commercially available. Among the problems encountered are the failure of adequate in vitro growth of some rotavirus strains, the uncertainty as to which strain(s) should be incorporated into a vaccine, the lack of a good experimental animal model system and a lack of effective efficacy studies in humans.
One recent approach to the development of a rotavirus vaccine involved the use of a live attenuated strain of a calf rotavirus which is immunologically distinct from human rotavirus strains, but which protects against human rotavirus infection, mainly of type I. It was found in one study that after oral immunization with such a vaccine, a severe case of diarrhea occurred prior to establishment of immunity. This was caused by a wild type rotavirus strain which interacted with the vaccine strain via gene reassortment to cause formation of a new reassortment virus. In other studies, although protection rates against diarrhea were over 80%, the protection rates against wild gastrointestinal infection and the seroconversion rate in vaccinated individuals were considerably lower. Moreover it has not been determined whether this vaccine can be effective against other rotavirus serotypes.
Other rotavirus vaccine programs include the use of a rhesus monkey rotavirus strain which is serologically related to human rotavirus type 3, and future studies are being designed to isolate a reassortment virus or viruses which contains the gene responsible for the type-specific antigen common to all four rotavirus serotypes.